1. Field of the Invention
The present invention relates to improvements in multi-stage rocket motors having utility for powered flight in air, beyond the atmosphere, or in hydrospace.
2. Description of the Prior Art
Proposals have been made in the prior art for increasing the useful energy of multi-stage rocket motors to the end that they may have greater range or greater capability in boosting heavy payloads. One proposal that has been made, as described in U.S. Pat. No. 3,301,184 granted Jan. 31, 1967 to F. K. Reinstein et al., is to eliminate that portion of the lower or first stage rocket motor case that would normally complete the pressure vessel at the forward end thereof. Specifically, the forward end of the first stage case is made substantially continuous in form with the nozzle of the second stage. The second stage is totally loaded with propellant, even into the nozzle associated therewith, so that the propellant is continuous from the forward end of the first stage into the second stage. The second stage of the motor is automatically ignited by terminal combustion of the first stage. Also, the stage separation mechanism that is provided is arranged such that stage separation is automatically effected after ignition of the second stage has taken place. With this arrangement, a considerable saving in weight of inert parts is said to be realizable. In particular, the weight of the forward end of the first stage case is eliminated, the ignition device for the second stage is eliminated, and the weight of the electrical equipment associated with ignition of the second stage is eliminated.
As described in U.S. Pat. No. 3,301,184, however, there are certain disadvantages to this prior art rocket motor arrangement due primarily to the fact that solid propellants do not have sufficient structural strength to contain the operating pressure of the first stage without some reinforcement. Pressure created by the combustion of the first stage is transmitted to the second stage. This causes the second stage case to enlarge and permit cracking of the propellant or extrusion of burning propellant from the first stage into the second stage prematurely. This may cause malfunction of the rocket motor in several ways. Specifically, (a) the thrust of the first stage may become erratic as a result of the burning surface thereof being deformed, (b) cracking of the second stage propellant may cause the stage to explode because of the greatly increased burning surface, and/or (c) the second stage may ignite prematurely. It is further stated that this kind of rocket eliminates the possibility that the second stage may be anything but 100% loaded with solid propellant, thus precluding a solid propellant rocket motor having a central combustion chamber for the second stage.
In order to overcome the above-mentioned disadvantages, U.S. Pat. No. 3,301,184 teaches the use of a lightweight pressure barrier, with a built-in explosive fuse, fitted in the forward end of the first stage case with none of the second stage propellant extending into the nozzle associated therewith. This is said to make possible all of the savings in weight of the rocket motor, as above described, and in addition permits use of a solid propellant rocket motor having a central combustion chamber for the second stage.
It has been found, however, that such an arrangement, as described in U.S. Pat. No. 3,301,184, is subject to a disadvantage that makes the rocket unsuitable particularly for large thrust applications. This disadvantage stems from the second or upper stage propellant having insufficient strength to withstand without deformation the compressive stresses to which it is subjected when large thrusts are produced by the associated first or lower stage. In order to enable the second or upper stage propellant to withstand such compressive stresses, the practice of the prior art has been to increase the thickness of the wall of the case containing the second and upper stage propellant, and consequently, the weight of the rocket. This detracts from the useful energy of the rocket.
Thus, there exists a need and a demand for further improvement in the method of and apparatus employed for increasing the useful energy of multi-stage rockets. The present invention was devised to fill the technological gap that has existed in the art in this respect.